Voltage-power booster for an operational amplifier

ABSTRACT

A voltage-power booster for an operational amplifier employs positive and negative voltage amplifier circuits connected to the positive and negative voltage supply terminals of the operational amplifier to produce output voltages for positive and negative signals which exceed the rated output voltage of the operational amplifier.

United States Patent [191 Gonda June 18, 1974 VOLTAGE-POWER BOOSTER FOR AN OPERATIONAL AMPLIFIER [75] Inventor: Tsunemi Gonda, Kawasaki, Japan [73] Assignee: Nippon Kogaku K.K., Tokyo, Japan [22] Filed: Dec. 12, 1972 [21] Appl. No.: 314,358

[30] Foreign Application Priority Data Dec. 21), I97! Japan 46402592 [52l lLS. (fl 330/22, 330/15, 330/24, 323/23 [51 Int. Cl. H03f 3/68 [58] Field of Search 323/23, 25; 307/31, 35, 307/52; 330/141, 69 C, 22 C, 30 D [56] References Cited UNITED STATES PATENTS 3,469,203 9/1969 Potras i. 330/84 9/1969 Beelitz 330/30 D 2/1972 Torok 323/23 X Primary ExaminerNathan Kaufman Attorney, Agent, or Firm-Shapiro and Shapiro [5 7] ABSTRACT 5 Claims, 5 Drawing Figures iP' OUTPUT TrS t I REE PATENTEDJUNI 81974 PRIOR ART FEG. i

W PRIOR ART FIG. 4

FIG. 3

FIG. 5

VOLTAGE-POWER BOOSTER FOR AN OPERATIONAL AMPLIFIER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a voltage-power booster for an operational amplifier.

2. Description of the Prior Art There are two conventional types of power boosters for providing power greater than the rated output of an operational amplifier, namely, the emitter-follower type and the complementary type. The emitterfollower type of power booster is effective only for a single output current polarity, whereas the complementary type of power booster is effective for both positive and negative output currents. With both types of boosters power amplification is provided by current amplification. no voltage amplification being effected. It is therefore impossible to obtain an output voltage greater than the rated output voltage of the operational amplifier (usually, of the order of volts).

For this reason, where a greater voltage is required, a voltage amplifier circuit must be added to the output of the operational amplifier. Such voltage amplifier circuits usually require a number of complex elements and must be designed independently of the operational amplifier. Different types of operational amplifiers may require entirely different voltage amplifier circuits depending upon the characteristic of the operational amplifier.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to solve the above-noted problems by providing a voltage-power booster which produces positive and negative voltages greater than the rated output voltage of the operational amplifier with which the booster is combined and which does not require the usual types of voltage amplifiers connected to the output terminal of the operational amplifier.

In accordance with the present invention, a voltagepower booster is combined with an operational amplifier and includes voltage amplifiers connected to the positive and negative voltage supply terminals of the operational amplifier and connected together to pro vide a new output terminal for the operational amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS The above object and other features of the present invention will become fully apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 diagrammatically shows a conventional power booster circuit of the emitter-follower type;

FIG. 2 diagrammatically shows a conventional power DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a conventional power booster of the emitter-follower type. An npn transistor Trl is connected as an emitter-follower and the base of said npn transistor Trl is connected with the usual output terminal of an operational amplifier OP], so that the output terminal Tfl of the emitterfollower provides the output terminal of a new operational amplifier including the emitter-follower. This arrangement is effective only for a positive output current since the transistor used is a npn type.

FIG. 2 shows a conventional power booster of the complementary type. Complementary npn and pnp transistors Tr2 and Tr3 have their bases connected with the usual output terminal of an operational amplifier 0P2, and their emitters connected together, so that an output terminal Tf2 is provided for a new operational amplifier including the transistors. This arrangement is effective to provide both positive and negative output currents.

Both types of prior art power boosters suffer from the problems noted previously.

Referring now to FIG. 3, there is shown a circuit arrangement according to an embodiment of the present invention. A Zener diode Dzl has its anode connected with the positive voltage source tenninal Tp of an operational amplifier 0P3. The Zener voltage Vzl of the Zener diode D21 is selected to be approximately equal to the difference between the positive voltage source (+V)'and the rated source voltage Vop of the operational amplifier 0P3 (i.e., Vzl z V Vop). The function of the Zener diode D21 is to permit application to a later-described transistor Tr4 of a positive source voltage greater than the rated source voltage Vop of the operational amplifier 0P3 and to apply the rated source voltage Vop to the operational amplifier 0P3. Instead of the Zener diode Dzl, a new voltage source may be connected between PI and Tp, for example, in such a manner that the positive and negative terminals thereof are connected with PI and Tp, respectively, the voltage VB of the new voltage source being selected to satisfy the condition VB z V Vop. Where very great voltage amplification is not required, the Zener diode Dzl may be eliminated and PI and Tp may be connected directly together. In this latter case, the positive source voltage +V is of course selected to a level approximately equalto the rated source voltage Vop of the operational amplifier 0P3, unlike the previously described cases, where the positive source voltage +V is substantially higher than Vop. The cathode of the Zener diode D21 is connected with one end P! of a resistor RDl while the positive voltage source +V is connected with the other end of the resistor. A pnp transistor Tr4 has its base connected with said end PI of the resistor RDl, is emitter connected with the positive voltage source +V via resistor RE], and its collector connected with terminal P3. These elements RDl, Dzl, RBI and Tr4 together constitute a positive voltagepower amplifier circuit.

A Zener diode D22 has its cathode connected with the negative voltage source tenninal TN of the operational amplifier 0P3. The Zener voltage Vz2 of the Zener diode D22 is approximately equal to the difference between the negative source voltage V and the rated source voltage V0p of the operational amplifier 0P3 (i.e., Vz z I VI VopI For the same reason as that described with respect to the Zener diode Dzl, the Zener diode Dz2 may be either replaced by a new voltage source or eliminated. The anode of the letter diode D22 is connected with one end P2 of a resistor RD2 while the negative voltage source V is connected with the other end of the resistor. An npn transistor TrS has its base connected with one end P2 of the resistor RD2, its emitter connected with the negative voltage source -V via resistor R152, and its collector connected with terminal P3. These elements RD2, D22, RE2 and TrS together constitute a negative voltagepower amplifier circuit. The output terminal T out of the operational amplifier OP3.is grounded through a load resistor RL. The load resistor RL is substantially equal to the rated load resistance of the operational amplifier 0P3. Terminal P3 is connected to the new output terminal T13 of the new operational amplifier provided with a voltage-power booster.

Operation of the above-described circuit will now be described. It is assumed that the new operational amplifier is utilized in an adder circuit, a subtractor circuit or an inverter circuit to supply an input voltage. Even for a zero input, there flows through the resistors RD! and RD2 a certain constant current i determined by the characteristics of source voltages +V, V, Zener diodes D21, D22, resistors RD], RD2 and operational amplifier 0P3. As a result, a predetermined voltage drop occurs across the resistors RDl and RD2. On the other hand, no current flows through the load resistor RL. By selecting equal values for resistances of the resistors RDl and RD2, for resistances of the resistors RBI and RE2 and for the Zener voltages Vzl and V22 of the Zener diodes D21 and D22, the potential at the terminal P3 will become zero if the input voltage is zero.

If the input voltage is made positive or negative, a positive current i or a negative current i,,,, respectively,

will flow through the load resistor RL in the direction 3 of the arrows in accordance with the positive or negative sign of the input voltage, respectively. It will be apparent from the usual properties of the operational amplifier that the load current i or i is variable substantially in proportion to the input voltage. Further, the

flow of such load current varies the current flowing through the resistor RD] or RD2, so that a voltage variation proportional to the input voltage occurs across the resistor RDl or RD2. Such voltage variation is applied to transistor Tr4 and Tr5 for amplification.

More specifically, a voltage variation induced at the terminal Pl by the positive current i is amplified by the transistor Tr4. Thus, an output current i corresponding to the voltage variation at the terminal P1 is supplied by the transistor Tr4. During that time, the 5 transistor Tr5 remains substantially non-conductive.

Similarly, a voltage variation produced at the terminal P2 by the negative current i is amplified by the transistor Tr5. As a result, an output current 1),, corresponding to the voltage variation at the terminal P2 is supplied by the transistor Tr5. During that time, the transistor Tr4 remains substantially non-conductive. Therefore, the amplitude of the output voltage provided from the output terminal Tj3 will be substantially 6 equal to that of the source voltage I i V l i Vopl l Vz] Also, where the Zener diodes D21 and D22 are eliminated as mentioned previously, the amplitude of the output voltage provided from the output terminal Tf3 will be substantially equal to that of the source voltage I i V f I Vop l.

According to the present invention, an output voltage greater than the rated output voltage of the operational amplifier 0P3 can be provided from the output terminal Tf3, which means that voltage amplification has been effected. As a result, the present invention can provide a voltage and power booster of high efficiency and can utilize voltage with a very high efficiency.

If it is desired to obtain a still greater output power, the transistor Tr4 in FIG. 3 may be replaced by a complementary connection of a pair of pup and npn transistors Tr6 and Tr? as shown in FIG. 4, and the transistor T15 by a Darlington connection of two npn transistors Tr8 and Tr9. In these cases, it will be apparent that the transistors Tr7 and Tr9 are power transistors.

A practical application of the FIG. 3 embodiment is shown in FIG. 5, which illustrates an inverter-amplifier with a gain of 100. in this figure, the resistor elements of FIG. 3 are designated as by 3300 for resistors RDl, RD2, 1K!) for resistors REl, RE2, and 3.3 K!) for resistor RL. The Zener voltage of the Zener diodes is Vzl V22 z 2.4V and the source voltage I Vl l VI 40V. Further, a resistor of IOOKQ is connected between the terminal P3 and the inverting input terminal of the operational amplifier 0P3 to apply a negative feedback. A resistor of lKQ is further connected between the inverting input terminal and the input terminal Pin. A capacitor C of small capacitance is parallelconnected with the IOOKQ resistor as indicated by a broken line. The capacitor C may be provided, if required, to prevent oscillation which might occur in some types of operational amplifiers.

In this embodiment, it is possible to obtain a voltagepower booster capable of high rate voltage utilization whose output amplitude is 78V (peak-to-peak) and a fraction.

The present invention as described above has the following advantages:

I. It can provide a voltage-power booster for an operational amplifier which provides an output voltage of great amplitude without interfering with the usual characteristics of the operational amplifier;

2. The number of elements in use is reduced, to a great economical advantage; and

3. Utilization of the gain not only of the operational amplifier but also of the voltage amplifier transistors enables a great deal of negative feedback to be applied, which results in improved linearity and stability.

Various types of operational amplifiers may be provided with boosters in accordance with the invention without requiring specially designed and complex voltage amplifiers connected in cascade with the operational amplifier. Merely for purposes of illustration, the operational amplifier may be a type 709 or a type LMlOl described on pages 10-24 through 10-26 of Handbook of Semiconductor Electronics, Third Edition, McGraw-Hill Book Co., 1970.

I claim:

I. A combination of an operational amplifier and a voltage-power booster therefor, including:

an operational amplifier;

a load resistor having one end thereof connected with the output terminal of said operational amplifier and the other end grounded;

a first voltage source having the negative terminal thereof grounded;

a first resistance element having one end thereof connected with the positive terminal of said first voltage source and the other end connected with the positive voltage source terminal of said operational amplifier;

a pnp transistor having the base terminal thereof connected with said other end of said first resistance element, the emitter terminal of said pnp transistor being connected with the positive terminal of said first voltage source, the collector terminal of said pnp transistor being operative as the output terminal of said booster;

a second voltage source having the positive terminal thereof grounded;

a second resistance element having one end thereof connected with the negative terminal of said second voltage source and the other end connected with the negative voltage source terminal of said operational amplifier and an npn transistor having the base thereof connected with said other end of said second resistance element, the emitter terminal of said npn transistor being connected with the negative terminal of said second voltage source, the collector terminal of said npn transistor being connected with the collector terminal of said pnp transistor.

2. A combination according to claim 1, wherein the voltages of said first and second voltage sources are greater than the rated source voltage of said operational amplifier, and said combination further includes:

first voltage dropping means connected between the positive voltage source terminal of said operational amplifier and said other end of said first resistance element, said first voltage dropping means causing a voltage drop between the positive voltage source terminal of said operational amplifier and said first resistance element so that a voltage approximately equal to the rated source voltage of said operational amplifier may be applied to the positive voltage source terminal of said operational amplifier; and

second voltage dropping means connected between said other end of said second resistance element and the negative voltage source terminal of said operational amplifier, said second voltage dropping means causing a voltage drop between the negative voltage source terminal of said operational amplifier and said second resistance element so that a voltage approximately equal to the rated source voltage of said operational amplifier may be applied to the negative source voltage terminal of said operational amplifier.

3. A combination according to claim 2, wherein said first voltage dropping means is a Zener diode having the cathode thereof connected with said other end of said first resistance element and the anode thereof connected with the positive voltage source terminal of said operational amplifier, and said second voltage dropping means is a Zener diode having the cathode thereof connected with the negative voltage terminal of said operational amplifier and the anode thereof connected with said other end of said second resistance element.

voltages of said two Zener diodes are equal. 

1. A combination of an operational amplifier and a voltage-power booster therefor, including: an operational amplifier; a load resistor having one end thereof connected with the output terminal of said operational amplifier and the other end grounded; a first voltage source having the negative terminal thereof grounded; a first resistance element having one end thereof connected with the positive terminal of said first voltage source and the other end connected with the positive voltage source terminal of said operational amplifier; a pnp transistor having the base terminal thereof connected with said other end of said first resistance element, the emitter terminal of said pnp transistor being connected with the positive terminal of said first voltage source, the collector terminal of said pnp transistor being operative as the output terminal of said booster; a second voltage source having the positive terminal thereof grounded; a second resistance element having one end thereof connected with the negative terminal of said second voltage source and the other end connected with the negative voltage source terminal of said operational amplifier and an npn transistor having the base thEreof connected with said other end of said second resistance element, the emitter terminal of said npn transistor being connected with the negative terminal of said second voltage source, the collector terminal of said npn transistor being connected with the collector terminal of said pnp transistor.
 2. A combination according to claim 1, wherein the voltages of said first and second voltage sources are greater than the rated source voltage of said operational amplifier, and said combination further includes: first voltage dropping means connected between the positive voltage source terminal of said operational amplifier and said other end of said first resistance element, said first voltage dropping means causing a voltage drop between the positive voltage source terminal of said operational amplifier and said first resistance element so that a voltage approximately equal to the rated source voltage of said operational amplifier may be applied to the positive voltage source terminal of said operational amplifier; and second voltage dropping means connected between said other end of said second resistance element and the negative voltage source terminal of said operational amplifier, said second voltage dropping means causing a voltage drop between the negative voltage source terminal of said operational amplifier and said second resistance element so that a voltage approximately equal to the rated source voltage of said operational amplifier may be applied to the negative source voltage terminal of said operational amplifier.
 3. A combination according to claim 2, wherein said first voltage dropping means is a Zener diode having the cathode thereof connected with said other end of said first resistance element and the anode thereof connected with the positive voltage source terminal of said operational amplifier, and said second voltage dropping means is a Zener diode having the cathode thereof connected with the negative voltage terminal of said operational amplifier and the anode thereof connected with said other end of said second resistance element.
 4. A combination according to claim 3, further including a third resistance element connected between the positive terminal of said first voltage source and the emitter terminal of said pnp transistor, and a fourth resistance element connected between the negative terminal of said second voltage source and the emitter terminal of said npn transistor.
 5. A combination according to claim 4, wherein the resistance values of said first and second resistance elements are equal, the resistance values of said third and fourth resistance elements are equal, and the Zener voltages of said two Zener diodes are equal. 